Method and apparatus for power conversion and regulation in a power converter having a plurality of outputs

ABSTRACT

Techniques are disclosed to control a power converter with multiple output voltages. One example regulated power converter includes a an energy transfer element coupled between a power converter input and first and second power converter outputs. A switch is coupled between the power converter input and the energy transfer element such that switching of the switch causes a first output voltage to be generated at the first power converter output and a second output voltage to be generated at the second power converter output. A current in the energy transfer element is coupled to increase when a voltage across the energy transfer element is a difference between an input voltage at the power converter input and the first output voltage. The current in the energy transfer element is coupled to decrease when the voltage across the energy transfer element is a sum of the first and second output voltages.

BACKGROUND

1. Technical Field

The present invention relates generally to electronic circuits, and morespecifically, the invention relates to circuits in which there is powerregulation.

2. Background Information

Electrical devices need power to operate. Many electrical devices arepowered using switched mode power converters. Some switched mode powerconverters are designed to provide multiple output voltages. Onechallenge with power converters of this type is to provide positive andnegative DC output voltages. Known power converters of this type oftenrely on fixed values of Zener diodes to set the output voltages, whichincreases costs and limits the flexibility of such power converters.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention detailed illustrated by way of example and notlimitation in the accompanying Figures.

FIG. 1 is a schematic that shows generally an example functional blockdiagram of a switching regulator with a positive and a negative outputreferenced to an input return in accordance with the teaching of thepresent invention.

FIG. 2 is a schematic that shows generally example shunt regulators thatindependently regulate currents in response to changes in outputcurrents to maintain desired output voltages included in an exampleregulator in accordance with the teaching of the present invention.

FIG. 3 is a schematic that shows generally example shunt regulatorsincluded in an example regulator in accordance with the teaching of thepresent invention.

FIG. 4 is a schematic that shows generally an example regulator circuitin accordance with the teaching of the present invention.

DETAILED DESCRIPTION

Examples related to power supply regulators are disclosed. In thefollowing description, numerous specific details are set forth in orderto provide a thorough understanding of the present invention. It will beapparent, however, to one having ordinary skill in the art that thespecific detail need not be employed to practice the present invention.Well-known methods related to the implementation have not been describedin detail in order to avoid obscuring the present invention.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the present invention. Thus, theappearances of the phrases “for one embodiment” or “in an embodiment” invarious places throughout this specification are not necessarily allreferring to the same embodiment. Furthermore, the particular features,structures, characteristics, combinations and/or subcombinationsdescribed below and/or shown in the drawings may be combined in anysuitable manner in one or more embodiments in accordance with theteachings of the present invention.

As will be discussed, some example power supply regulators in accordancewith the teachings of the present invention utilize switched mode powerconversion that provide two output voltages of opposite polarity withrespect to a common reference that is the input return. Examples of thedisclosed power supply regulators may be used in a variety ofapplications in which positive and negative direct current (DC) outputvoltages are provided from a higher input voltage without an isolationtransformer. The example methods disclosed can provide two regulatedoutput voltages at lower costs than other known methods. Moreflexibility is provided by the disclosed power supply regulators andmethods in the selection of output voltages than by other known methodsthat rely on fixed values of Zener diodes to set output voltages. Sometarget applications for the disclosed power supply regulator and methodsare those that do not require galvanic isolation between input andoutput, such as power supplies for major household appliances.

To illustrate, FIG. 1 is a functional block diagram that shows anexample generalized power converter or switching regulator 100 inaccordance with the teachings of the present invention with a positiveand a negative output 160 and 165, respectively, referenced to the inputreturn. As shown, a DC input voltage V_(G) 105 is coupled to switch S₁115, which is controlled by control circuit 170. In the variousexamples, control circuit 170 includes circuitry to employ any of avariety of switching techniques including at least one of a constantfrequency pulse width modulation (PWM), variable frequency PWM, on/offcontrol or the like. An energy transfer element, which is illustrated asinductor L₁ 125, is coupled between switch S₁ 115 and the outputs of theregulator circuit 100. In the illustrated example, the outputs are shownas output voltage V₁ 160 across load impedance Z₁ 150 and output voltageV₂ 165 across load impedance Z₂ 155. Capacitor C₁ 140 is illustrated asbeing coupled across load impedance Z₁ 150 and capacitor C₂ 145 isillustrated as being coupled across load impedance Z₂ 155. As shown inthe illustrated example of FIG. 1, the outputs are each coupled to aground terminal coupled to both load impedance Z₁ 150 and load impedanceZ₂ 155.

In operation, DC input voltage V_(G) 105 is converted to output voltageV₁ 160 across load impedance Z₁ 150 and output voltage V₂ 165 acrossload impedance Z₂ 155 by the action or switching of switch S₁ 115 inresponse to a control circuit 170. In the illustrated example, controlcircuit 170 causes switch S₁ 115 to switch among three positions. Whenswitch S₁ 115 is in position G, the current I_(L) 130 in inductor L₁ 125is the same as the input current I_(G) 110 supplied from the inputvoltage V_(G) 105. When switch S₁ 115 is in position F, the currentI_(L) 130 in inductor L₁ 125 is the same as freewheeling current IF 120derived from an output of the power converter as shown. When switch S₁115 is in position X, the current I_(L) 130 in inductor L₁ 125 is zero.In the illustrated example, control circuit 170 switches switch S₁ 115between positions G, X, and F with sequence and durations to regulateone output. In one mode of operation, (continuous conduction mode) theswitch S₁ 115 spends no time at position X. The single regulated outputmay be V₁ 160, V₂ 165, or a combination of both.

In operation, the switching of switch S₁ 115 produces currents I_(L)130, I_(G) 110, and I_(F) 120 that contain triangular or trapezoidalcomponents. Capacitors C1 140 and C2 145 filter currents I_(L) 130 andI_(F) 120 respectively, which produce the respective DC output voltagesV₁ 160 and V₂ 165 that have small alternating current (AC) variationsrelative to their DC values. Load impedances Z₁ 150 and Z₂ 155 produceload currents I₁ 135 and I₂ 137 from the respective output voltages V₁160 and V₂ 165.

For the regulator of FIG. 1, switch S₁ 115 may be controlled to regulateonly a single output voltage. The other output voltage will change withload currents I₁ 135 and I₂ 137. To regulate more than one outputvoltage requires a current regulator to regulate current I₁ 135 or I₂137 in response to changes in output voltages V₁ 160 and V₂ 165. In theillustrated example, control circuit 170 is shown having three inputsincluding an input coupled to an end of load impedance Z₁ 150, an inputcoupled to an end of load impedance Z₂ 155 and an input coupled to aground terminal.

In one example of the power converter or power supply regulator 100,control circuit 170 is not included or is instead adapted to switch SI115 in a fixed pattern, which produces unregulated output voltages V₁160 and V₂ 165. In this example, current I_(L) 130 through inductor L₁125 increases when the voltage across inductor L₁ 125 is the differencebetween the input voltage V_(G) 105 and output voltage V₁ 160, which iswhat occurs when switch S₁ 115 is in position G. Continuing with thisexample, the current I_(L) 130 through inductor L₁ 125 decreases whenthe voltage across inductor L₁ 125 is the sum of output voltage V₁ 160and output voltage V₂ 165, which is what occurs when switch S₁ 115 is inposition F.

FIG. 2 shows generally a power converter or power supply regulator 200,which includes shunt regulators 205 and 210 coupled across loadimpedances Z₁ 150 and Z₂ 155, respectively. In the illustrated example,shunt regulators 205 and 210 independently regulate currents I₁ 135 andI₂ 137 in response to changes in output currents I_(Z1) 235 and I_(Z2)240 to maintain the desired output voltages in accordance with theteachings of the present invention. In various examples, only one ofshunt regulators 205 or 210 may be necessary depending how loadimpedances Z₁ 150 and Z₂ 155 might change. In operation, shuntregulators 205 or 210 only add to the current in the loads if the loadimpedances Z1 150 or Z2 155 are insufficient to maintain the desiredoutput voltage. In the example shown in FIG. 2, power supply 200includes power supply regulator 100 of FIG. 1 with the addition of shuntregulators 205 and 210. As shown in FIG. 2, control circuit 170 switchesswitch S₁ 115 to regulate an output voltage V_(O) 245, which is the sumof V₁ 160 and V₂ 165.

In the illustrated example, the ratio of voltages V₁ 160 and V₂ 165 isdetermined by the ratio of resistors R₁ 215 and R₂ 220 that are includedin respective shunt regulators 205 and 210. Transconductance amplifiers225 and 230 are included in shunt regulators 205 and 210, respectively,and produce unidirectional current from current sources I_(SH1) 250 andI_(SH2) 255 at their respective outputs to regulate voltages V₁ 160 andV₂ 165 across load impedances Z₁ 150 and Z₂ 155. In operation, if thereis a change in load to cause a decrease in either load current I_(Z1)235 or I_(Z2) 240, the control circuit will modify the switching ofswitch SI to maintain the value of output voltage V_(O) 245 inaccordance with the teachings of the present invention. Then currentsources I_(SH1) or I_(SH2), respectively, will increase to maintainoutput voltages V₁ 160 and V₂ 165 at the values determined by the ratioof resistors R₁ 215 and R₂ 220. In various examples, one or more ofshunt regulators 205 and 210 are included in an integrated circuit.

FIG. 3 shows generally one example of shunt regulators 205 and 210 ofFIG. 2 included in a power converter or power supply regulator 300 inaccordance with the teachings of the present invention. In theillustrated example, shunt regulator 205 includes resistor R₁ 215 andbipolar transistor 305 while shunt regulator 210 includes resistor R₂220 and bipolar transistor 310. In one example, transistors 305 and 310have a finite base to emitter voltage V_(BE) that causes the outputvoltages V_(O1) 315 and V_(O2) 320 to differ from the desired regulatedvalues of V₁ and V₂ by no more than V_(BE). In the example of FIG. 3,the regulation of V_(O1) and V_(O2) is described by the expressions:(V ₁ −V _(BE))≦V _(O1)≦(V ₁ +V _(BE))(V ₂ −V _(BE))≦V _(O2)≦(V ₂ +V _(BE))andV _(O1) +V _(O2) =V ₁ +V ₂ =V _(O)Therefore, the nonzero value of V_(BE) in the circuit of FIG. 3 preventsthe transistors from conducting simultaneously in accordance with theteachings of the present invention.

In the example illustrated in FIG. 3, it is appreciated that bipolartransistors 305 and 310 are illustrated as including single transistors.However it is appreciated that the teachings of the present inventionare not limited to single transistors and that additional transistors orother circuit elements may be added to bipolar transistors 305 and 310as appropriate such as for example Darlington transistor pairs or thelike to realize the desired circuit performance in accordance with theteachings of the present invention. In addition, it is noted that theexample illustrated in FIG. 3 shows both bipolar transistors 305 and 310included. However, in another example, it is noted that either bipolartransistor 305 or 310 may be eliminated if changes to the respectiveload do not demand current from both shunt regulators 205 and 210.

FIG. 4 is one example schematic showing generally the power converter orregulator circuit of FIG. 3 with increased detail. In particular, theexample of FIG. 4 shows switch S₁ 115 including a diode D₁ 410 and atransistor 445, which are included in an integrated circuit 405 with acontrol circuit 440. In the illustrated example, integrated circuit 405may be a LNK304 produced by Power Integrations, Inc. of San Jose, Calif.In the illustrated example, integrated circuit 405 is coupled betweenthe DC input voltage V_(G) 105 and the inductor L₁ 125. In anotherexample, integrated circuit 405 is not included and transistor 445 istherefore a discrete metal oxide semiconductor (MOSFET) or bipolartransistor and control circuit 440 is a separate controller inaccordance with the teachings of the present invention. Capacitor C₄ 435is a bypass capacitor coupled to the BP terminal of integrated circuit405 for the operation of integrated circuit 405. In the illustratedexample, control circuit 440 receives a signal proportional to theoutput voltage V_(O) that is on capacitor C₃ 430. Capacitor C₃ chargesto approximately the sum of output voltages V_(O1) 315 and V_(O2) 320when diode D₁ 410 in switch 115 conducts the freewheeling current I_(F)120. In operation, diode D₁ 410 automatically configures the switch S₁115 to position F when the diode D₁ 410 is conducting and to position Gor X when the diode D₁ 410 is not conducting.

In the foregoing detailed description, the methods and apparatuses ofthe present invention have been described with reference to a specificexemplary embodiment thereof. It will, however, be evident that variousmodifications and changes may be made thereto without departing from thebroader spirit and scope of the present invention. The presentspecification and figures are accordingly to be regarded as illustrativerather than restrictive.

1. A power converter, comprising: an energy transfer element coupledbetween a power converter input and first and second power converteroutputs; and a switch coupled between the power converter input and theenergy transfer element such that switching of the switch causes a firstoutput voltage to be generated at the first power converter output and asecond output voltage to be generated at the second power converteroutput, wherein a current in the energy transfer element is coupled toincrease when a voltage across the energy transfer element is adifference between an input voltage at the power converter input and thefirst output voltage, and wherein the current in the energy transferelement is coupled to decrease when the voltage across the energytransfer element is a sum of the first and second output voltages. 2.The power converter of claim 1 wherein the energy transfer elementcomprises an inductor coupled between the power converter input andfirst and second power converter outputs.
 3. The power converter ofclaim 1 wherein a first load impedance is to be coupled across the firstpower converter output and a second load impedance is to be coupledacross the second power converter output such that the first outputvoltage is across the first load impedance and the second output voltageis across the second load impedance.
 4. The power converter of claim 1further comprising a first capacitor coupled across the first powerconverter output and a second capacitor coupled across the second powerconverter output.
 5. The power converter of claim 1 wherein the firstand second outputs are coupled to a ground terminal.
 6. The powerconverter of claim 1 wherein the switch is adapted to be coupled in afirst position when the current in the energy transfer element iscoupled to increase when the voltage across the energy transfer elementis a difference between an input voltage at the power converter inputand the first output voltage, and wherein the switch is adapted to becoupled in a second position when the current in the energy transferclement is coupled to decrease when the voltage across the energytransfer element is the sum of the first and second output voltages. 7.A power converter, comprising: an energy transfer element coupledbetween a power converter input and first and second power converteroutputs; a switch coupled between the power converter input and theenergy transfer element such that switching of the switch causes a firstoutput voltage to be generated at the first power converter output and asecond output voltage to be generated at the second power converteroutput, wherein a current in the energy transfer element is coupled toincrease when a voltage across the energy transfer element is adifference between an input voltage at the power converter input and thefirst output voltage, and wherein the current in the energy transferelement is coupled to decrease when the voltage across the energytransfer element is a sum of the first and second output voltages; and acontrol circuit coupled to the switch to control a switching of theswitch to regulate an output voltage in response to the first and secondpower converter outputs.
 8. The power converter of claim 7 wherein thecontrol circuit is further coupled to a ground terminal.
 9. The powerconverter of claim 7 wherein the output voltage regulated by the controlcircuit is a sum of voltages across the first and second power converteroutputs.
 10. The power converter of claim 7 wherein the control circuitincludes circuitry to employ at least one of constant frequency pulsewidth modulation (PWM), variable frequency PWM, or on/off control. 11.The power converter of claim 7 wherein the energy transfer elementincludes an inductor.
 12. The power converter of claim 7 furthercomprising a first shunt regulator coupled across a first load impedancecoupled to the first power converter output.
 13. The power converter ofclaim 12 further comprising a second shunt regulator coupled across asecond load impedance coupled to the second power converter output. 14.The power converter of claim 12 wherein the first shunt regulatorcomprises a unidirectional transconductance amplifier coupled to thefirst power converter output to add unidirectional current at the firstpower converter output if the first load impedance is insufficient toregulate the output voltage.
 15. The power converter of claim 12 whereinthe first shunt regulator is included in an integrated circuit.
 16. Thepower converter of claim 12 wherein the first shunt regulator includes afirst bipolar transistor coupled across the first power converter outputand a first resistor coupled to the first bipolar transistor.
 17. Thepower converter of claim 13 wherein the first shunt regulator includesat least a first bipolar transistor coupled across the first powerconverter output and a first resistor coupled to the first bipolartransistor and wherein the second shunt regulator includes a secondresistor coupled the first resistor.
 18. The power converter of claim 17wherein the second shunt regulator further includes at least a secondbipolar transistor coupled to the second resistor.
 19. The powerconverter of claim 7 wherein the switch is coupled to set in one ofthree positions, wherein when the switch is in a first position, acurrent in the energy transfer element is the same as an input currentsupplied from the power converter input, wherein when the switch is in asecond position, the current in the energy transfer element is the sameas a freewheeling current from the power converter output, and whereinwhen the switch is in a third position, the current in the energytransfer element is zero.
 20. The power converter of claim 19 whereinthe switch comprises a switching transistor coupled between the powerconverter input and the energy transfer element and a control circuitcoupled to control the switching transistor in the integrated circuit inresponse to a signal proportional to the output voltage.
 21. The powerconverter of claim 20 wherein the switching transistor and the controlcircuit are included in an integrated circuit coupled between the powerconverter input and the energy transfer element.
 22. The power converterof claim 20 further comprising a diode coupled receive the freewheelingcurrent and coupled to the control circuit coupled to the switchingtransistor, coupled to configure the switch to the first position whenthe diode is conducting and to the second or third position when thediode is not conducting.